Discussion
Our findings illustrated differences in survival of different types of
epicardial leads; bipolar steroid-eluting leads had considerably better
survival rate than unipolar non-steroid-eluting ones, by more than 85%
lower risk of failure in 48 months. However, no other lead and patient
characteristics were revealed to be associated with lead failure. In
this order, epicardial leads function and survival was similar between
adults and children.
Epicardial lead implantation is preferable in small children, patients
with congenital heart disease with right-to-left shunts, intention to
preserve the venous access mainly in the ones with difficult
accessibility, and prevention of venous thrombosis. However, recent
advances in epicardial leads and developed bipolar steroid-eluting ones
have demonstrated improved early pacing and sensing thresholds, as well
as the long-term function of the lead, which is comparable with
endocardial ones.1,2,8
We illustrated that bipolar steroid-eluting epicardial leads remained
functional significantly better than unipolar non-steroid-eluting ones.
Some studies investigated bipolar and unipolar leads pacing
characteristics in the short-term, implying that the bipolar group had
fewer sensing and pacing failure.10,11 The probable
underlying mechanism has been declared to be related to the coaxial
design of Medtronic bipolar leads, which result in a lower chance of
stray signal pick up and better conduction
performance.10 Furthermore, the pacing threshold
illustrated to be more stable regarding bipolar steroid-eluting leads in
all chambers in the long-term.2 Our finding also
demonstrated that bipolar leads have better long-term pacing
characteristics because of the significant rise observed in pacing
threshold of unipolar leads in the right atrium and left ventricle but
not regarding bipolar group and significantly greater pacing threshold
of left ventricular unipolar leads at follow up. Meanwhile, primary
pacing characteristics or energy threshold (ET) which was a predictive
factor of lead failure in a study did not affected the lead survival in
the current study.1 On the other hand, the observed
difference between bipolar steroid-eluting and unipolar
non-steroid-eluting might be related to the variation of the steroid
elution. In this order, steroid-eluting leads were declared to have
better long-term functions.1,12
A closer look at the mechanism of steroid impact reveals that addition
of dexamethasone (steroid) to a lead can decrease inflammation of the
electrode-tissue interface, which is the responsible factor for the rise
in the acute pacing threshold. Furthermore, in the long-term, the
inflammation might result in the formation of a scar or fibrous capsule
in the electrode-tissue interface, which causes a higher pacing
threshold.13 Even though, it is noteworthy that
steroid elution leads have been shown not to be an influential factor in
a previous study in particular when comparing epicardial and endocardial
leads.14 It could be concluded that steroid elution
and being bipolar could be both associated with better long-term
function; however, more extensive studies that compare steroid elution
within bipolar and unipolar leads are needed to evaluate this.
The paced chamber was not a significant factor in its survival, as there
was no difference between pacing characteristics of leads on different
chambers, whether at discharge or at follow-up time or regarding bipolar
steroid-eluting and unipolar non-steroid-eluting leads, which is
consistent with previous studies.1 However, the pacing
threshold significantly increased regarding unipolar non-steroid-eluting
leads on the left ventricle or right atrium, but not on the right
ventricle, probably due to the sample population, since there was an
increase in pacing threshold in the right ventricular unipolar
non-steroid-eluting leads but not statistically significant.
Our findings indicated that epicardial leads implemented in adults and
children were not significantly different in long-term function.
Consistent with our results, adults and children with previous CHD were
compared in a study that showed no difference in epicardial and
endocardial survival regarding age groups.15 Although
in that study, bipolarity and steroid elution were not investigated
separately, the lead type (bipolar and unipolar) adjusted analysis of
age variable in the current study similarly was not correlated with lead
survival. In contrast, the longevity of a lead function was
significantly better in over 12-year-old children compared with younger
ones.14 Therefore, investigating lead characteristics
within children might change the results; however, we did the same
analysis, which showed no association between age groups among children
and better survival.
Congenital heart defect which is an indication for epicardial lead
implantation observed in half of our study population but was not
associated with the long-term function of a lead.1,2However, a study on patients with endocardial and epicardial leads in
pediatrics illustrated that congenital heart defect is a significant
predictive of lead failure in both type of the leads, which mostly
resulted in failure due to exit block.14
In this study, we compared the survival of bipolar steroid-eluting leads
with unipolar non-steroid-eluting ones, which is pivotal for deciding
about the type of lead to be used, particularly in patients that
endocardial leads are not applicable. Also, the function of epicardial
leads is not different between adults and children; thus, they could be
used in both groups, despite much of the previous studies that
investigated their longevity in children only.
We encountered some limitations due to patients who were not presented
for regular follow up, or not at specific time. However, this centre is
referral and patients who present from various regions in the country,
usually prefer to get their follow up in their living area and refer to
this centre in case of pacemaker problems and failures. Therefore, it
could be assumed that their pacemaker was functional during the time of
their absence. Furthermore, to solve this limitation, we called these
patients and completed their follow up by receiving their documents as
much as possible.